Optical recorders have been used for recording video signals as well as other forms of information-bearing signals. Many of the recorders use but a single laser and a single beam of light. A disadvantage to such single-beam optical signal recorders is that the recording cannot be immediately verified; to verify signal recording requires an additional rotation of the optical record disk.
Some optical signal recorders, particularly for making masters of video disks, have employed two-laser systems, one laser providing a beam for recording or writing information onto the record disk, while a second laser provides a light beam for sensing the just-recorded information. Optical elements combine the read and write beams such that the read beam immediately follows the writing beam for effecting, almost simultaneous, read-after-write verification. Typically, a two-laser systems requires that the writing laser and the reading laser operate at different wave lengths, and thus were supported in separate housings. Such separation imposes critical alignment and adjustment procedures, particularly where high density optical recording is desired. Thermally-induced changes in dimensions also create stability problems.
Accordingly, it is desired to provide a simpler apparatus which facilitates the independent adjustment of the lasers and their respective associated optical elements, such as collimating lenses and the like, while avoiding thermal gradient problems. It is also desired to minimize the size of the assembly such that a compact optical signal recorder is achievable, yet one that provides extremely high areal density recording.